1. Field of the Invention
The present invention relates to glass having a low thermal expansion useful as heat-resisting glass and various substrate materials and also to a method of manufacturing the same.
2. Background of the Invention
Glass having a low thermal expansion has been used in wide areas including the field of substrate material, heat resisting glass, etc. in precision machines and instruments and also in the field of substrate material for display in case it is without alkali.
A commonly known glass having low thermal expansion is a borosilicate glass. As to the representative one thereof, #7740 manufactured by Corning has been known and its average linear thermal expansion coefficient is 32.5×10−7° C.−1 at 0 to 300° C.
However, in the glass having such a low thermal expansion, melting temperature of the glass material for the manufacture of glass is usually very high.
Therefore, in the manufacture of such a glass, there have been problems such as that working ability lowers, cost for the manufacturing equipments becomes high and cost for maintenance of the manufacturing equipments becomes high.
When melting property of glass is improved for solving such problems, an average linear thermal expansion coefficient tends to become high. In the properties of glass, low thermal expansion and low-temperature melting are usually in a conflicting relation each other and development of glass exhibiting both of the two characteristics has been difficult.
On the other hand, glass having a low thermal expansion has been demanded in broad fields and, therefore, there has been a demand for glass which has both of low thermal expansion and low-temperature melting property and is able to manufacture at a low cost.
As a glass for a liquid crystal display, Patent Document 1 discloses a glass where an average linear thermal expansion coefficient at 30° C. to 380° C. is 33 to 49 (×10−7° C.−1) and temperature corresponding to viscosity of 102.5 poises which is a high-temperature viscosity of glass is 1499° C. to 1595° C. However, in its Examples where an average linear thermal expansion coefficient is relatively low, the above temperature is high and there is no disclosure for Example of glass having both low thermal expansion and low-temperature melting property.
Patent Document: Gazette of Japanese Patent Laid-Open No. 2001/261,366